PCT refresh in a rolling window scenario requires partitioning at the top level on some level from the time dimension. sales table is partitioned by time_id column and products is partitioned by the prod_id column. If PCT refresh is being done for a table which has join dependent expression in the materialized view, then data modifications should not have occurred in any of the join dependent tables. Data modifications can only occur on the partitioned table. SQL> create materialized view mv 2 --build deferred 3 refresh fast on demand 4 with primary key 5 enable query rewrite 6 as 7 select a.rowid erowid,b.rowid drowid ,b.dname, a. Example 6-6 Materialized View Using UNION ALL with Joins and Aggregates. 2 Replies Latest reply Latest reply Any DML operation, such as an INSERT, or DELETE, UPDATE, or DDL operation on any dependency in the materialized view will cause it to become invalid. With approximately hundreds of different products in each product category, including the partitioning key column prod_id of the products table in the materialized view would substantially increase the cardinality. The following examples illustrate creation of fast refreshable materialized views involving UNION ALL. Hi, Your tutorial really helps to understand PCT well, we have issue with materialized view logs when truncating base table partition that contains 200million rows every time, we do truncate on master table partition daily. PCT refresh is also not enabled on the materialized view Action: Use just REFRESH, which will reinstantiate the entire table. Consider an example of a materialized view storing daily customer sales. To revalidate a materialized view, use the ALTER MATERIALIZED VIEW COMPILE statement. You can achieve this through partition change tracking (PCT), which is a method to identify which rows in a materialized view are affected by a certain detail table partition. This compile process is quick, and allows the materialized view to be used by query rewrite again. Partitioning the fact tables improves scalability, simplifies system administration, and makes it possible to define local indexes that can be efficiently rebuilt. Partitioning a materialized view involves defining the materialized view with the standard Oracle partitioning clauses, as illustrated in the following example. times is not a partitioned table. This is because the data is already protected by the VPD policies against the relations in the request query. This is because times_y table is joined indirectly through times_m and times_d tables to sales table on its partitioning key column time_id. To support PCT, a materialized view must satisfy the following requirements: At least one of the detail tables referenced by the materialized view must be partitioned. Table 6-1 shows the four levels of each dimension. Query rewrite does not use its full and partial text match modes with request queries that include relations with active VPD policies, but it does use general rewrite methods. If the materialized view is on a prebuilt container, the creator, if different from the owner, must have SELECT WITH GRANT privilege on the container table. Because I created a materialized view log on that table, PCT fast refresh is enabled on the SH.MV_PCT_SALES materialized view. Using Query Rewrite with Virtual Private Database, Restrictions with Materialized Views and Virtual Private Database. The COMPILE clause of the ALTER MATERIALIZED VIEW statement can be used when the materialized view has been invalidated. And in order to use this new feature we have to enable it a materialized view level: SQL> alter materialized view DEMO_MV enable on query computation; Materialized view altered. SQL> create materialized view mv 2 --build deferred 3 refresh fast on demand 4 with primary key 5 enable query rewrite 6 as 7 select a.rowid erowid,b.rowid drowid ,b.dname, a. In addition to this, PCT is enabled on products table because of presence of its partitioning key column prod_id in the materialized view. When a materialized view is partitioned on the partitioning key column or join dependent expressions of the detail table, it is more efficient to use a TRUNCATE PARTITION statement to remove one or more partitions of the materialized view during refresh and then repopulate the partition with new data. At this point, because cust_dly_sales_mv has PCT available on table sales using a partition key, Oracle can identify the stale rows in the materialized view cust_dly_sales_mv corresponding to sales_part3 partition (The other rows are unchanged in their freshness state). Because of the large volume of data held in a data warehouse, partitioning is an extremely useful option when designing a database. This materialized view is eligible for query rewrite because the ENABLE QUERY REWRITE clause has been included. Materialized views is a very old feature (you may remember that it was called snapshots a long time ago). When a materialized view is partitioned on the partitioning key column or join dependent expressions of the detail table, it is more efficient to use a TRUNCATE PARTITION statement to remove one or more partitions of the materialized view during refresh and then repopulate the partition with new data. For PCT refresh, if the materialized view is partitioned appropriately, this will use TRUNCATE PARTITION to delete rows in the affected partitions of the materialized view, which is faster than a delete. Enable or disable its use for query rewrite. All other changes are achieved by dropping and then re-creating the materialized view. "string" Cause: The materialized view log does not exist or cannot be used. It is possible and advantageous to track freshness to a finer grain than the entire materialized view. An expression consisting of columns from tables directly or indirectly joined through equijoins to the partitioned detail table on the partitioning key and which is either a dimensional attribute or a dimension hierarchical parent of the joining key is called a join dependent expression. This enables partition change tracking on products table with significantly less cardinality impact than grouping by the partition key column prod_id. In addition, you can include a predicate in the WHERE clause of the materialized view that embodies the effect of the VPD policy. Since Oracle 12.2, it is possible to create Real-Time Materialized Views with the option ENABLE ON QUERY COMPUTATION. Users who access the materialized view are subject to the VPD policy on the materialized view. The expression calendar_year_name from times_y table is a join dependent expression and the tables times_d, times_m and times_y are join dependent tables. Using materialized views with Virtual Private Database is similar. prod_yr_sales_mv includes the DBMS_MVIEW.PMARKER function on the products table in its SELECT list. If you do not want to use PCT refresh, you can just partition by list on GROUPING_ID column. You can: Change its refresh option (FAST/FORCE/COMPLETE/NEVER). Further, the materialized view must include a constant column (known as a UNION ALL marker) that has a distinct value in each query block, which, in the following example, is columns 1 marker and 2 marker. For example, instead of using one, long materialized view, you could create the following materialized views: By using two materialized views, you can incrementally maintain the materialized view my_groupby_mv.
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